Abstract
The complicated geological conditions will bring great challenges to the drillstring of horizontal wells for the reason that the increase of the well depth in SichuanChongqing region. Since drillstring failure and friction during drilling are generally caused by drillstring vibration, great importance must be attached to computer simulation methods for the prediction of drillstring vibration. A finite element model considering axial, lateral and torsional vibration is established. In order to verify the established numerical model, an indoor experimental device based on the similarity principle was established. The vibration characteristics of three shale gas horizontal wells drillstrings are described. The reasons for the large difference in vibration characteristics between the three wells were discussed by changing the well structure, BHA(bottom hole assembly) and drilling parameters. The simulation results show that the depth of ultra-deep well 3 is only 1.27 times of that of medium-deep well 2, but the fluctuation of WOB (weight on bit) is 2.8 times. The primary factor for the great difference of WOB fluctuation is the change of vertical section depth, the secondary factor is the change of the horizontal section length. Additionally, the reasonable range of speeds has been proposed and applied in the field. The advantage of this numerical analysis method is that it can judge the vibration and friction torque of drillstring in horizontal wells with arbitrary structure, drilling parameters and BHA. This method has certain guiding significance to the field practice.
Highlights
With the development of shale gas, coalbed gas and other new hydrocarbon resources, drilling engineering is facing more complex formation environment
Dynamic WOB simulation results show that the depth of ultra-deep well 3 is only 1.27 times of that of medium-deep well 2, but the fluctuation of WOB is 2.8 times
The results show that the transient maximum value, average value and fluctuation amplitude of the friction torque increase with the increase of the well depth
Summary
With the development of shale gas, coalbed gas and other new hydrocarbon resources, drilling engineering is facing more complex formation environment. Feng et al [Feng, Vadali, Ma et al (2017)] proposed a sixdegree-of-freedom finite element model to describe drillstring dynamics It mainly focuses on the eccentricity of BHA, mud damping, bit-rock interaction and their coupling mechanism. The friction and fluid-solid coupling between drill string and borehole wall are considered in the model He found that the bit-bounce can be achieved by applying larger rotational speeds and axial loads. The horizontal wells in the SichuanChongqing region are usually around 7,000 m, the vertical depth is mostly 4,000 m, and the horizontal section length is about 1000-1500 m, which may even be longer in the future In this oil and gas area, engineering problems such as drillstring failure and friction caused by excessive vibration often occur. The conclusion of this study is of guiding significance for practical drilling
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